The present invention relates to satellite multi-carrier burst communication systems and methods, and, more particularly, to such systems and methods in which a low-cost, fixed output power radio is operated with fixed gain to provide improved system performance.
Generally, in satellite communication systems, earth transmission stations modulate a video, audio or data signal and transmit the signal to an orbiting satellite. The satellite then relays the information to a receiving antenna in a different location. Each earth transmission station in the system typically uses one or more channel unit modules which output a 70 Mhz intermediate frequency output. This hardware module connects to a user voice or data interface, and performs voice end coding/decoding, channel coding/decoding, and modulation/demodulation functions.
The earth transmission station utilizes an outdoor unit, which operates as an amplifier to amplify the L-band channel unit output and converts it to C/Ku/other band before it is fed to a transmission antenna.
In single-carrier satellite communication systems, the outdoor unit operates at a fixed power level and incorporates a method of power control unique to the unit. In a multi-carrier communication system, up to four channel units are linked together in a chassis to allow up to four calls to be in progress at any one time. Previously, applications that required fixed gain operation used an outdoor unit radio specifically designed for fixed gain operation in a multi-carrier environment. Such a radio is expensive relative to a fixed output radio for a single carrier environment. However, the cost of the outdoor unit is prohibitively expensive for many conventional satellite communication systems. Furthermore, the currently available multi-carrier outdoor unit does not guarantee a constant gain in relation to temperature and other site-to-site environmental factors. The unit also does not compensate for variations in the gain characteristics of the cables and other equipment used for connecting indoor equipment with outside equipment during operation of the system. Such changes occur due to temperature, humidity and other environmental factors. Furthermore, the initial installation of such systems is complicated because various site-to-site differences are inherent in the gain due to the use of different cable lengths, connectors, and other hardware items that also vary from site-to-site.
In order to reduce expense, a multi-carrier system can utilize the traditional, low-cost, single carrier outdoor unit. The single carrier outdoor unit has the advantage of guaranteeing a constant gain in relation to temperature, unlike its more expensive counterpart. The low-cost outdoor unit, however, does not allow each individual channel unit the ability to transmit over the satellite at different power levels. The low-cost outdoor unit can regulate its own output power, but cannot compensate for the various power levels of the channel units during transmissions. Consequently, a new method of power control is needed to use such an outdoor unit with a multi-carrier system.
Therefore, there is a need for a method for using a low-cost, fixed output power radio in a multi-carrier burst-mode communication application which allows the radio to operate with fixed gain, thereby preserving the amplitude relationships among the various signals output by system.
Furthermore, there is a need for a method of monitoring and controlling the gain of an outdoor unit used in a multi-carrier satellite communication system.